Implantable blood pumps may be used to provide assistance to patients with late stage heart disease. Blood pumps operate by receiving blood from a patient's vascular system and impelling the blood back into the patient's vascular system. By adding momentum and pressure to the patient's blood flow, blood pumps may augment or replace the pumping action of the heart. For example, a blood pump may be configured as ventricular assist device or “VAD.” Where a VAD is used to assist the pumping action of the left ventricle, the device draws blood from the left ventricle of the heart and discharges the blood into the aorta.
To provide clinically useful assistance to the heart, blood pumps impel blood at a substantial blood flow rate. For an adult human patient, a ventricular assist device may be arranged to pump blood at about 1-10 liters per minute at a differential pressure across the pump of about 10-110 mm Hg, depending on the needs of the patient. The needs of the patient may vary with age, height, and other factors.
During operation, the differential pressure across the pump may increase. This increase of differential pressure may be harmful to the patient, and may be indicative of either a suction condition or occlusion within the pump. Therefore, it would be desirable to provide a blood pump controller which can monitor the differential pressure across the pump and can control operation of the pump in order to avoid harmful pressure buildups.
Operation of some blood pumps may be controlled in response to a determined flow rate at the pump. For example, pending U.S. Publication No. 2012/0245681, the disclosure of which is hereby incorporated herein in its entirety, describes a method of operating a blood pump using a control circuit that detects a low flow condition, characterized by a low flow rate, and commands a drive circuit of the pump to cause a momentary reduction in the pump speed in order to cure the low flow condition. Although clearance of the low flow condition may have the further benefit of reducing differential pressure across the blood pump, it is possible to encounter a pressure buildup across the pump before a low flow condition is detected. Therefore, it would be further desirable to be able to prevent pressure build up in the blood pump without having to detect a low flow condition.